Add text field change handling for autofill preview in textarea element.

public/web/WebAutofillClient.h

Index: public/web/WebAutofillClient.h
diff --git a/public/web/WebAutofillClient.h b/public/web/WebAutofillClient.h
index 8b13aa0c156330d76999cbcbbf4797d5bb032231..5a14e4f8d79b8eef108558778fb8b658a8d89a8f 100644
--- a/public/web/WebAutofillClient.h
+++ b/public/web/WebAutofillClient.h
@@ -33,6 +33,7 @@
 
 namespace blink {
 
+class WebFormControlElement;
 class WebFormElement;
 class WebFrame;
 class WebInputElement;
@@ -49,6 +50,7 @@ public:
     // These methods are called when the users edits a text-field.
     virtual void textFieldDidEndEditing(const WebInputElement&) { }
     virtual void textFieldDidChange(const WebInputElement&) { }
+    virtual void textFieldDidChange(const WebFormControlElement&) { }
     virtual void textFieldDidReceiveKeyDown(const WebInputElement&, const WebKeyboardEvent&) { }
     // This is called when a datalist indicator is clicked.
     virtual void openTextDataListChooser(const WebInputElement&) { }